Method and device for simulating radio channel

ABSTRACT

The invention relates to a method and device for performing channel simulation, the device comprising a set of channel simulation units ( 200  to  214 ) for simulating a radio channel, each unit comprising radio frequency parts ( 200 A to  214 A) and baseband parts ( 200 B to  214 B). In the solution of the invention, the baseband parts of several different units ( 200  to  214 ) are arranged to simulate the same channel.

FIELD OF THE INVENTION

The invention relates to a method and a device implementing the methodfor simulating a radio channel. The invention relates especially toimplementing a multi-path radio channel simulator.

BACKGROUND OF THE INVENTION

One essential problem in radio systems is the rapid variation of theproperties of a radio channel with time. This relates especially tomobile systems, in which at least one of the participants in aconnection is often mobile. The attenuation and impulse response of theradio channel then vary within a wide phase and amplitude range eventhousands of times per second. The phenomenon is random by nature, somathematically it can be described by statistical means. The phenomenoncomplicates the design of radio connections and the used devices.

There are many reasons for the variation in a radio channel. Whentransmitting a radio frequency signal from a transmitter to a receiverin a radio channel, the signal propagates along one or more paths, ineach of which the phase and amplitude of the signal vary, which causesfades of different lengths and strengths in the signal. In addition,noise and interference from other transmitters also disturbs the radioconnection.

A radio channel can be tested either under actual conditions or using asimulator that simulates the actual conditions. Tests conducted inactual conditions are difficult, because tests taking place outdoors,for instance, are affected for example by the weather and season thatchange all the time. Even measurements taken in the same place produce adifferent result at different times. In addition, a test conducted inone environment (city A) does not fully apply to a second correspondingenvironment (city B). It is also usually not possible to test the worstpossible situation under actual conditions.

However, with a device simulating a radio channel, it is possible tovery freely simulate a desired type of a radio channel between two radiodevices in such a manner that the radio devices operate at their naturaltransmission rates, just like in an actual operating situation. FIG. 1illustrates an example of a device for simulating a radio channel. Thefigure shows a first set of devices 100 to 108 and a second set ofdevices 110 to 118, and a channel simulator 120. The first set oftransmitters 100 to 108 can comprise mobile phones, for instance, thatthrough their antenna connectors are connected to the inputs of thechannel simulator 120. The second set of devices 110 to 118 can in turnbe receivers of base station equipment that are connected to the outputsof the channel simulator. The number of the first and second devicesneed not be the same. In the example of the figure, there are fivedevices in each set.

A channel simulator typically comprises several channel elements thatare capable of simulating and modelling a desired channel type. Thechannel simulator of FIG. 1 comprises eight elements. Each elementcomprises both a radio frequency part and a baseband part. A signal canbe fed to the input of the channel simulator either in radio frequencyor baseband format. In the latter case, the radio frequency parts of thechannel elements are bypassed. In the radio frequency part, a signal isconverted to baseband, and the resulting baseband signal is forwarded tothe baseband parts, in which the impact of the channel fade is added tothe signal.

In prior-art solutions, the channel element forms a fixed unit. As inthe case of FIG. 1, there may be situations during simulation, in whichnot all channel elements are used, because there are fewer channels tosimulate than the device has capacity for.

BRIEF DESCRIPTION OF THE INVENTION

One object of the invention is thus to implement a method and a deviceimplementing the method in such a manner that the capacity of a channelsimulator can be utilized optimally in different situations and that thesimulator can easily be updated. This is achieved by a method forsimulating a radio channel, in which the radio channel is simulated bymeans of channel elements that comprise a radio frequency part and abaseband part and in which a signal of one radio frequency part isprocessed in more than one baseband part.

The invention also relates to a device for performing channelsimulation, which comprises a set of means for simulating a radiochannel, each means comprising radio frequency parts and baseband parts.In the device of the invention, the baseband parts of several differentmeans are arranged to simulate the same channel.

Preferred embodiments of the invention are disclosed in the dependentclaims.

The invention is based on the idea that each baseband part is capable ofconnecting the baseband part inputs and outputs to adjacent basebandparts. In a digital radio channel simulator, the channel is modelled inthe baseband parts with a FIR (Finite Impulse Response) filter thatforms a convolution between the channel model and the input signal insuch a manner that the signal that is delayed by different delays isweighted by channel coefficients, i.e. tap coefficients, and theweighted signal components are summed. The channel coefficients arealtered to correspond to the behaviour of an actual channel. By enablinga flexible distribution of the baseband parts, multiple signalpropagation paths in the channel can be simulated, if necessary.Multiple propagation paths require multiple FIR taps, and by combiningdifferent baseband parts in the solution according to the preferredembodiments of the invention, it is possible to achieve a higher numberof taps than in prior-art solutions.

When the simulation to be performed is defined in a channel simulator,i.e. its parameters, such as the number of channels to simulate, thenumber and connections of input and output signals, are fed in, acontrol unit of the channel simulator optimises the use of the simulatorequipment on the basis of the parameters. If all radio frequency unitsof the equipment are not needed during the simulation, the basebandunits corresponding to them can be utilized during the simulation. Thecontrol unit controls the connections of the input and output signals ofthe baseband units so that several baseband parts simulate the samechannel, and thus, the full capacity of the equipment is utilized.

In a preferred embodiment of the invention, the baseband part is dividedinto two separate modules, an interface module that comprises the inputand output parts of the baseband part and a digital module thatcomprises the component needed for the actual channel modelling, such asthe FIR filter. By thus dividing the baseband part into two differentmodules, significant advantages are gained in the maintenance andupdatability of the device.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in more detail by means of preferredembodiments and with reference to the attached drawings, in which

FIG. 1 shows the general structure of a channel simulator that wasalready described above,

FIG. 2 illustrates in more detail an example of the structure of achannel simulator,

FIG. 3 is an example of the structure of a baseband part,

FIG. 4 is a flow chart showing an example of a solution of anembodiment, and

FIGS. 5A and 5B illustrate examples of different connections.

DETAILED DESCRIPTION OF THE INVENTION

Let us examine the channel simulator of FIG. 2. The simulator compriseseight channel elements 200 to 214, each of which is made up of a radiofrequency part 200A to 214A and baseband part 200B to 214B. Each radiofrequency part comprises a radio frequency input signal from atransmitter and an output signal to a receiver 200C to 214C. Thesimulator further comprises a local oscillator divider 216 that receivesas input one or more radio frequency local oscillator signals 218. Thedivider 216 divides a suitable radio frequency signal 220 to 234 foreach radio frequency unit 200A to 214A.

In the radio frequency units 200A to 214A, the signals from thetransmitter are converted to baseband for instance by multiplying themby a local oscillator signal, after which the baseband signal 200D to214D is forwarded to the baseband units. A baseband signal 200E to 214Earrives from the baseband units to the radio frequency units through thesimulated channel and is converted back to radio frequency in the radiofrequency units and transmitted to the receiver.

In the baseband units 200B to 214B, the impact of the channel fade isadded to the signal. This is typically done by FIR filters. The desiredform of the channel is achieved by adjusting the tap coefficients of theFIR filter. The channel simulator comprises a simulator control unit(SCU) 236 that controls the tap coefficients of the FIR filters of thebaseband units by means of a control bus 238. The simulator control unitalso controls the operation of the entire simulator by means of acontrol bus 240. Information on simulation parameters, such as frequencyparameters, gains and the like, are transmitted prior to the simulationover the control bus to the different parts of the device.

The channel simulator further comprises control means 242 that controlthe operation of the entire simulator. The control means are preferablyimplemented by means of a processor or computer and suitable software.The processor can naturally be replaced by a programmable logic made upof separate components. The control means further comprise interfaceequipment, such as a display and keyboard, by means of which thesimulation parameters can be entered into the device. The parameterstypically comprise the number of transmitters, the number of receivers,the number of channels to be simulated and their properties. The controlmeans 242 control the simulator through the simulation control unit 236.The simulation control unit 236 also comprises an input and output 244of a synchronization signal, by means of which several channelsimulators can be synchronized. Thus, several devices can be connectedparallel to implement a wide simulation.

The baseband units of the channel simulator also comprise connectionsbetween each other. A signal coming from the radio frequency unit thathas not yet passed through the FIR filter is connected from eachbaseband unit to the adjacent baseband units, preferably to the inputsof the FIR filters in these units. These connections are illustrated inFIG. 2 by connections 248 to 260. Further, from each baseband unit a FIRfilter output signal is connected to the adjacent baseband units,preferably to be summed in the outputs of the FIR filters in theseunits. These connections are illustrated in FIG. 2 by connections 262 to274.

The channel simulator can also operate directly on baseband, in whichcase conversions to and from baseband are not necessary in the radiofrequency units. A radio-frequency, analogue or digital signal can befed as an input signal to the channel simulator.

FIG. 3 illustrates the structure of a baseband unit according to apreferred embodiment of the invention. The baseband unit 202B of FIG. 2is used as an example. The baseband unit is divided into two separatemodules, i.e. a interface module 300 that comprises the input and outputparts of the baseband part and a digital module 302 that comprises thecomponents required in the actual channel modelling. An analogue 304 ordigital 306 transmitter signal arrives at the interface module as inputfrom the radio frequency unit. The signal comprises separate I-branchand Q-branch signals. Analogue inputs 304 are forwarded through low-passfilters 308 and 310 to analogue-to-digital converters 312.

The digital I and Q signals 314 are next forwarded to a multiplexer 316in the digital module 302. Digital-format I and Q signals 248 to 250arrive as other inputs to the multiplexer from the adjacent basebandunits. Correspondingly, the I and Q signals are forwarded as outputs 248to 250 to the adjacent baseband units.

The multiplexed I and Q signals are FIR filtered in a known manner,whereby the impact of the channel is added to the signals. The I and Qsignals are first forwarded to a set of delay elements 318 to 324, thedelay of each of the elements being separately settable. The signalsthat have been delayed in different ways are forwarded from the delayelements to complex FIR filter elements 326 to 332. The control bus 238from the simulation control unit sets the tap coefficients of the FIRelements, the control bus being transmitted to the FIR elements ascontrol data 336 through a bus adapter 334. The outputs of the FIRelements are summed in adders 338 to 344, to which the outputs 262 ofthe FIR elements of the adjacent baseband units are also brought forsumming through a multiplexer 346. The sum total 264 is taken onward tothe adjacent baseband elements. The sum is also forwarded to theinterface module 300 and from there on either directly in digital formatout 348 or through digital-to-analogue converters 350 and low-passfilters 352, 354 in analogue format 256 out to the radio frequency unit.

In a preferred embodiment of the invention, the control bus 240 from thesimulation control unit controls the multiplexers 316 and 346, by meansof which connections between different baseband units are adjusted.

In a preferred embodiment of the invention, the channel simulation meansof the baseband units are thus divided so that the simulation means ofseveral different baseband parts can simulate the same channel. Let usexamine the flow chart shown in FIG. 4 that illustrates the method stepsof an embodiment. In this example, it is assumed that the devicestructure is modular, i.e. the configuration of the device can bealtered between different types of simulations to suit each simulation.

In step 400, current is switched on to the device. After this, in step402, the control means 242 of the device check the current configurationof the device. This way, the control means know what the configurationof the device is, i.e. of which modules the device is constructed. Instep 404, simulation parameters are received from the user. This ispreferably done by means of suitable interface software, a display and akeyboard. The simulation parameters typically comprise the number oftransmitters, the number of receivers, the number of channels to besimulated and their properties. The number of transmitters and receiversis not always the same when a test environment comprises transmission orreception diversity, for instance, or possible interfering transmitters.

In step 406, the control means 242 define, on the basis of theparameters, the connections between the channel elements of the deviceand transmit the necessary commands to the channel elements by means ofthe simulation control unit 236 and bus 240. If it turns out, forinstance, that there are fewer channels to be simulated than there arechannel elements in the device, the system knows that all radiofrequency units will not be used and the baseband units corresponding tothe unused ones can then be connected parallel to the baseband unitscorresponding to the used radio frequency units to assist in the channelsimulation. Which baseband unit is connected where is selected on thebasis of the simulation parameters. For instance, if there is one radiochannel to simulate, whose modelling requires several FIR taps, severalbaseband units can be allocated for this calculation. The channels whosesimulation is simple require no extra calculation capacity.

In step 408, the control means 242 transmit, prior to simulation,information on the simulation parameters, such as frequency parametersand gains, to different parts of the device by means of the simulationcontrol unit 236 and along the control bus 240. In step 410, simulationis performed according to the given parameters. The simulation controlunit 236 controls the FIR filter taps by means of the bus 238.

FIGS. 5A and 5B illustrate two examples of different connections in thesame equipment but with different simulation parameters. FIG. 5A shows asituation where two radio frequency units 200A and 214A are used. Fromthe first radio frequency unit 200A, the signal is connected to fivebaseband units 200B to 208B. From the second radio frequency unit 214A,the signal is connected to three baseband units 210B to 214B. From thebaseband units, the output signal is taken back to the radio frequencyunits. To clarify the figure, the receiving radio frequency units 500Aand 514A are drawn separate.

FIG. 5B shows a situation where two radio frequency units 200A and 214Aare used as signal sources and four radio frequency units 500A, 506A,508A and 514A are used as signal receivers. In this example, basebandunits are connected in a versatile manner between differenttransmitter/receiver radio units. This way, one and the same physicalconfiguration provides versatile simulation environments in such amanner that the equipment can be efficiently utilized.

Even though the invention has been explained in the above with referenceto examples in accordance with the accompanying drawings, it is apparentthat the invention is not restricted to them but can be modified in manyways within the scope of the attached claims.

1. A device for performing channel simulation comprising: a plurality ofsimulation means, each one of the plurality of simulation meansincluding a corresponding one of a plurality of radio frequency partsand a corresponding one of a plurality of baseband parts, each of theplurality of basebands part being connected to another one of theplurality of baseband parts, and selected ones of the plurality ofbaseband parts being configured to simulate one of a plurality of radiochannels.
 2. The device as claimed in claim 1, wherein the devicecomprises a control means configured to connect inputs and outputsassociated with each of the of baseband parts in such a manner thatselected ones of the plurality of baseband parts are configured toperform a simulation of the same radio channel.
 3. The device as claimedin claim 2, wherein the control means is configured to connect theinputs and outputs of each of the plurality of baseband parts based onat least one parameter of the simulation being performed.
 4. The deviceas claimed in claim 2, wherein the control means is arranged to connectthe inputs and outputs of the plurality of baseband parts, and theplurality of radio frequency parts that are not needed during thesimulation.
 5. The device as claimed in claim 2, wherein the inputs andoutputs of the modeling means of the digital module corresponding toeach of the plurality of baseband parts is connected to inputs andoutputs of a digital module of an adjacent one of the plurality ofbaseband parts.
 6. The device as claimed in claim 1, wherein each of theplurality of baseband parts comprise: an interface module comprisinginputs and outputs of a respective one of the plurality of basebandparts; and a digital module comprising means for modeling a radiochannel.
 7. A method for simulating a radio channel, comprising:simulating at least one radio channel by means of a plurality of channelelements, each one of the plurality of channel elements including acorresponding one of a plurality of radio frequency parts and acorresponding one of a plurality of baseband parts, each of theplurality of baseband parts being connected to another one of theplurality of baseband parts, and selected ones of the plurality ofbaseband parts being configured to process a signal of one of theplurality of radio frequency parts.
 8. The method as claimed in claim 7,the method further comprising: selecting connections of inputs andoutputs associated with the plurality of baseband parts of differentones of the plurality of channel elements based on at least oneparameter of a simulation being performed.
 9. The method as claimed inclaim 8, wherein the connections are to the plurality of baseband partsand the plurality of radio frequency parts that are not needed duringthe simulation.
 10. The method as claimed in claim 8, wherein a channelmodel affects the connections.
 11. The method as claimed in claim 8,wherein a number of the plurality of channel elements used in thesimulation affect the connections of the inputs and outputs of theplurality of baseband parts of different ones of the plurality ofchannel elements.
 12. The method as claimed in claim 8, wherein a numberof transmitters and receivers are used in the simulation and theconnections between the transmitters and receivers affect theconnections of the inputs and outputs of the plurality of baseband partsof different ones of the plurality of channel elements.
 13. The methodas claimed in claim 8, wherein a number of channel elements in thedevice affects the connections of the inputs and outputs of theplurality of baseband parts of different ones of the plurality ofchannel elements.
 14. The method as claimed in claim 7, comprising:checking a configuration of a simulator device after activation;receiving at least one simulation parameter from a user; selecting aconnection of inputs and outputs associated with the plurality ofbaseband parts of different ones of the plurality of channel elementsbased on at least one parameter of a simulation being performed; settingsets the at least one simulation parameter used in different parts ofthe device; and performing the simulation according to the at least oneparameter.
 15. A device for performing channel simulation comprising: aplurality of radio channel simulators, each one of the radio channelsimulators comprising a corresponding one of a plurality of radiofrequency parts and a corresponding one of a plurality of basebandparts, each of the plurality of baseband parts being connected toanother one of the plurality of baseband parts, and selected ones of theplurality of baseband parts being configured to simulate one of aplurality of radio channels.